[wip] Allow static self-referential struct type fields in interfaces

[max-charlamb]

Treat static struct type fields in interfaces as self-referential, similar to static struct type fields inside of structs.

Resolve #104511

[JakeYallop]

Will this also resolve

public struct MyStruct
{
    static ImmutableArray<MyStruct> One;
}

which is also mentioned in the issue as causing a type load exception (a separate issue was closed as a duplicate), but has nothing to do with interfaces.

[kg]

Will this also resolve

public struct MyStruct
{
    static ImmutableArray<MyStruct> One;
}

which is also mentioned in the issue as causing a type load exception (a separate issue was closed as a duplicate), but has nothing to do with interfaces.

That's a different-but-similar problem that might be fixable by making some additional changes to this self-referential type check. We'll look into it.